The recent expansion of the bio-fuels industry has fueled the popularity of ethanol and the effects of ethanol on the environment, economy and US national policy. Antibiotics have been used in fermentations during the production of fuel alcohol since its inception dating back to the 1970's. The co-products (distiller's grains) resulting from these fermentations have been fed to livestock increasingly over the past 3 decades with a particularly sharp increase of 340% from 1999 to 2005 to 8.35 million metric tons of distiller's grains in the United States alone. Most (98%) of the distiller's grains in North America come from plants that produce ethanol for oxygenated fuels.
Alcohol is produced by yeast fermentation, primarily of carbohydrates derived from starch-based or sugar-based feedstocks. This fermentation is provided by yeast, specifically the microorganism Saccharomyces cerevisea that ferments the available carbohydrates to produce ethanol. The entire process of alcohol production is well documented in “The Alcohol Text Book”, 4th edition, Jacques, Lyons & Kelsall, published by Nottingham University Press, 2003, which is incorporated herein by reference.
One of the important concerns with a conventional fermentation system is the difficulty of maintaining a sterile condition free from contaminating bacteria in the large-sized batches during the long fermentation period. Unfortunately, the optimum atmosphere for fermentation is also extremely conducive to bacterial growth. Should a batch become contaminated, not only must the fermentation mixture (i.e. the yeast, feedstock, nutrients, water, etc.) be discarded, but the entire fermentation vessel must be emptied, cleaned and sterilized, adding unwanted costs and loss of production.
It is common in current commercial fermentation processes that contaminating bacteria will infect the fermentations and consume the available carbohydrate to produce organic acids consequently causing less carbohydrate availability to the preferred yeast fermentation. Contamination by bacteria is very costly to the ethanol producer and a variety of control methods are utilized to limit this event. It is commonplace in most ethanol producing facilities to utilize caustic washing via clean in place systems.
The origin of these contaminants is multi-faceted and is being researched by researchers and producers alike. However, it is generally accepted that much of the bacteria originates from the incoming feedstock since the starch crops are often contaminated with bacteria from the field and storage silos. Jet cooking the fermentation substrate (mash) helps lower the bacteria count, but does not completely eliminate the contaminants as this process is not a sterilization procedure and bacteria contamination is unavoidable as these production facilities are not sterile production environments like those commonly found in the pharmaceutical industry.
The increased popularity of the bio-fuels industry, along with the increased supply of distiller's co-products, has caused heightened awareness and concerns regarding antimicrobials being used during the fermentation process as the antimicrobials may “carry through” to the resulting distiller's co-products.
The industry is currently awaiting more direct guidance from the FDA (Food & Drug Administration) and the CVM (Center for Veterinary Medicine) as well as certain state agencies (where applicable) on the allowable use of antimicrobials as a processing aid in ethanol production
Therefore, an economical method to selectively control contaminating bacteria is needed. The method must utilize smaller amounts of an antibiotic then currently being used to target and act bactericidal and/or bacteristatic to control contaminating bacteria in a fermentation, such as a bacterial contaminant found in the production of fuel alcohols, beverage alcohols and industrial alcohols while improving production yield. Additionally, distiller's co-products of the fermentation must be safe for direct feeding to animals, i.e., the antibiotic used must not be detectable in the distiller's co-products so as to comply with increasing state and federal regulation. From the alcohol producer's point of view, the antibiotic needs to be cost effective and would be of more value if it did not have a deleterious effect on the yeast, thus producing more alcohol. Further, the antibiotic needs to be less susceptible to resistance by the targeted bacteria and be effective in low concentrations while not carrying through to the distiller's grains.